1. Field of the Invention
The present invention relates to screening or testing for prostate specific antigen (PSA). More specifically, the present invention relates to a method for screening for PSA from whole blood spotted on a solid support. Additionally, the present invention relates to a test kit for screening or testing for PSA using the solid support.
2. Description of the Prior Art
Prostate adenocarcinoma accounts for the majority of malignancies in males over the age of 65. Yearly screening for prostate cancer is recommended after the age of 45. There has been considerable effort toward identifying suitable prostate cancer markers to assist in screening and diagnosing this disease.
PSA is recognized as the most sensitive marker of prostatic adenocarcinoma (Brawer M K. Cancer 1993; 71 (suppl):899-905; Oesterling J E. J Urol 1991; 145:907-23). PSA is also recognized as a proven screening vehicle (Gann P H, et al. J Amer Med Assoc 1995; 273:289-94.; Catalona W J, et al. JUrol 1994; 151:1283-90). It is the most sensitive front line test for identifying prostate gland-contained, and hence presumably curable, cancer. PSA is also useful in detecting clinically significant tumors, as opposed to latent, indolent microcarcinomas. In fact, screening for PSA is even superior to the common office practice of digital rectal examination (DRE). For example, Labrie et al. (Clin Invest Med 1993; 16: 425-39) showed that 97% of cancers detected at annual follow-up by DRE plus PSA testing were PSA-positive. Thus, only a minimal benefit accrues from including DRE in the medical evaluation.
Prostate specific antigen has also been used to detect the onset of puberty in children between ages 8 and 25 years (Vieira J. G. H., et al. J Clin Endocrinol Metab 1994;78: 1185-1187). Since PSA is an androgen-dependent protein and its expression is up-regulated by androgenic steroid hormones, women with hyperandrogenic syndromes may also have elevated PSA in their serum. Additionally, PSA has now been found in the serum and extracts from breast tumors (Diamandis E. P., Yu H. J Clin Endocrinol Metab 1995;80:1515-1517), indicating that it has utility in breast cancer screening and monitoring.
Currently, PSA is tested by first collecting a blood specimen via venipuncture phlebotomy. This usually necessitates that the individual to be tested make a physician office or hospital visit. The blood so collected is usually processed for shipment to a suitable clinical diagnostic laboratory. In most cases, shipment necessitates first freezing serum or plasma, and shipping (on ice) the frozen specimen to the diagnostic testing laboratory. Hence, any means to simplify collecting and testing blood would facilitate the screening for prostate disease, and facilitate earlier detection and treatment.
Blood collected by capillary puncture from the heel, finger, or earlobe and dried on filter paper has been used advantageously in large scale infant screening programs throughout the world to detect inborn errors of metabolism and congenital defects (Dussault J H, et al. J Pediatr 1974; 86:670-4). Such filter paper techniques provide a suitable delivery system alternative in cases where transport delays, safety concerns, and high temperatures preclude the shipment of liquid whole blood to the diagnostic testing laboratory. Also, capillary puncture is less invasive and more convenient than venipuncture. Additionally, only minimal volumes of dried blood need be collected in this approach.
There has not heretofore been a method for using dried whole blood to test PSA. Additionally, there has not heretofore been a device for collecting a specimen onto a solid support for convenient shipment to a diagnostic laboratory. These and other disadvantages of the prior art are overcome by the present invention.